I only have room for three, so of course I have four. I'm trying to make them be as diverse as possible so I never get bored.
EM: Gottlieb Sing Along
SS: Bally Flash Gordon
Alphanumeric: Gottlieb Deady Weapon
DMD: Williams Whitewater
My own rule is that if a new pin I want ever comes up for sale nearby, I have to want it enough to replace whatever current pin sits in that category.